You're going to have to take the hull off for this one. It's not that bad of a job because the cable is easy to access with the hull removed.
Why does the steering cable need to be replaced?
I once had to replace the steering cable on my old 1996 SPX after I bent the living daylights out of the pump end. Working through those access holes in the older skis was awful. I found out NOT to try to use aftermarket parts, go genuine BRP. The aftermarket cable was really close but the ends were slightly different. Ended up having to pull the aftermarket cable out and reinstall a genuine BRP cable.